Christian Happ and his colleagues recruited 60 students (20 men) with varied video gaming experience and had them spend 15 minutes playing the violent and bloody beat-em-up game Mortal Combat vs. DC Universe on the Playstation 3. Some of the participants played the morally good character Superman, while the others played the Joker, the baddie from Batman. Apart from that, the game experience was the same for all participants – their time was spent in hand-to-hand combat against a variety of other computer-controlled game characters.

Another twist to the experiment was that before the game began half the participants read a bogus Wikipedia article about their character, designed to encourage them to empathise with him. For those playing Superman, the article said how he’d come from a loving family. The Joker article described how he’d suffered abuse in his childhood.

After playing the video game, the participants looked at grids of faces on a computer screen and indicated how hostile they looked. Some of the grids contained angry faces, but the crucial test was how hostile the participants rated the grids that contained all neutral faces. The key finding here was that participants who’d played the Joker were more likely to perceive hostility in neutral faces (a marker of an aggressive mindset), as compared with the participants who played Superman.

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These results show that the effects of playing a violent game aren’t straight-forward. Apart from anything else, the effects clearly depend on the moral nature of the fictional character that players embody. Note though, that we can’t say that playing as Superman actually boosted levels of prosocial behaviour because it’s possible rates of returning the letter were still lower for these students than they would have been had they not played the video game at all. It’s a shame there wasn’t a baseline control condition to shed light on this.

That the influence of this violent game varies according to the character played was made even more apparent by the back stories, which were designed to encourage empathy towards the characters. For those students who played as Superman and read about his childhood, their perception of hostility in neutral faces was lower than for those who didn’t read this detail. By contrast, students who played the Joker and who read about his upbringing were more likely to see hostility in neutral faces, as compared with those who didn’t read about his past. In other words, the effect of the violent game differed according to the character the students played, and this difference was amplified when they were encouraged to empathise with their character.

Think of reading or playing video games as priming. The effect is temporary, but it’s a priming nonetheless. And you can be temporarily primed for good actions or bad actions.